Siloxane elastomers



SILOXANE ELASTOMERS Keith E. Polmanteer, Midland, Mich., assignor to Dow Corning Corporation, Midland, Mich., a corporation of Michigan I No Drawing. Application January 7, 1957 I Serial No. 632,630 t Claims. (Cl; 260-37) material are many. For example, it reduces the cost of fabrication in that no heating is required- It removes any limitations as to the size of the article being fabricated since there is no necessity for heating. Also, it allows siloxane elastomers to be employed for uses in which artificial heating is impractical or impossible, for example,

' in the calking of voids in buildings, automative vehicles or in large electrical equipment.

The best previously known room temperature curing siloxane elastomers were those described in US. Patent 2,571,039. These materials were prepared by incorporating alkyl silicates into acid polysiloxanes, that is, polymeric siloxanes which had acid groups such as sulphate and phosphate groups in the siloxane polymer. Whereas such materials were suitable'for many uses they are not suitable for uses where a corrosion problem exists. Consequently, there was need for a satisfactory room temperature curing elastomer which would not contain corrosive materials.

It is an object of this invention to prepare a room temperature curing siloxane elastomer which is substantially free from bubbles in the cured state. Another object is to prepare a suitable electrical potting compound. Another object is to provide siloxane elastomershaving stress-strain properties higher. than any previously known 2,927,907 I Patented Mar. 8, 1960 nese inclusive in the electromotive series of metals, in

T which salt the acid radicals have less than 16 carbon atoms.

The acid-free siloxanes employed in this invention can contain attached to the silicon atoms any monovalent hydrocarbon radical and any halogenatedmonovalent hydrocarbon radical. Theterm acid-free as employed herein means that the siloxane polymer is free of acid groups such as =.SiAc, where Ac is, for example, Cl, The siloxanes employed in this invention are substantially diorgano sub stituted siloxanes which may contain limited amounts of monoorgano substituted siloxanes. Preferably the-siloxanes should be substantially free from triorganosiloxan'e units.

Specific examples of R groups'which are operative in this invention are alkyl groups such as methyl, ethyl and octadecyl; cycloaliphatic groups such as cyclohexyl and cylopentyl; aromatic hydrocarbon radicals such as phenyl, xenyl, and naphthyl; aralkyl groups such as benzyl; alkaryl groups such as tolyl and xylyl; unsaturated hydrocarbon radicals such as vinyl, allyl and cyclohexenyl and halogenated monovalent hydrocarbon radicals such as chloro- 'methyl, bromophenyl, tetrafluoroethyl, trifluorovinyl, trisiloxane elastomer. Another object is to prepare a calk' ing compound suitable for use in applications where no heat can be applied. Another object is to provide a selfcuring coating composition. Other objects and advantages will be apparent from the following description.

This invention relates to a room temperature curing composition of matter consisting essentially of (1) an organopolysilcmane of at least 100 cs. viscosity at 25 C.,

said siloxane being composed of polymer units of the J formula of a hydrocarbonoxy silicate in which therhydrocarbon radicals are monovalent aliphatic hydrocarbon radicals of lessthan 8 carbon atoms, and (3) trom .01 to 10% by weight based on the weight of the polysiloxane of a carboxylic acid salt of metals ranging fromlead to mangafluorotolyl, hexafiuoroxylyl, heptachloroxenyl, heptafluoropropyl, chlorodifluorovinyl, chlorohexafluorocyclopen- 'tenyl, l-bromo-S-tribromopropyl and It is to be understood that the siloxanes employed herein can be either homopolymeric materials or copolymeric materials containing two or more different types of siloxane units and further that both organic radicals attached to any one silicon atom can be the same or the radicals attached to any one silicon atom can be difierent.

- The polymeric siloxanes which are employed in-this invention can range in viscosity from cs. up. Thus,

such as coating or potting. When excellent stress-strain properties are desired it is preferable to employ-high molecular weight nonfiowing soluble gums. it is preferred that the polymers be soluble.

The silicates within the scope of this invention include In general,

any silicate wherein the organic radicals arethe defined hydrocarbonoxy radicals. The term silicate as employed herein includes both orthosilicates of the formula Si(OR) in which R is an aliphatic hydrocarbon radical a .of less than 8 and preferably less than 6 carbon atoms and partial hydrolyzates of such orthosilicates commonly 1 known as polysilicates. These polysilicates are polymeric materials in which the silicon atoms are linked through SiOSi linkages, the remaining valences of the silicon 'being satisfied by OR radicals in which R is as above defined. Preferably the polysilicates are nonvolatile materials, The devolatilization may be carried out by heating the polysilicate at reduced pressure at temperatures up to 250 C.

Both the orthosilicates and polysilicates employed in this invention are commercially available materials. Specific examples of such silicates are n-propylorthosilicate, amylorthosilicate, allylorthosilicate, pentenylortho-;

silicate, diethyldipropylorthosilicate, hexylorthosilicate, methylpolysilicate, ethylpolysilicate, isopropylpolysilicate, secondary amylpolysilicate. and n-butylpolysilieate and mixtures thereof. 'y

are lead, tin, nickel, cobalt, iron, cadmium, chromium,

zinc and manganese. Any carboxylic acid salt of these metals 'is operative in this invention-provided the carboxylic acid radical contains less than 16 carbon atoms. It is preferable that the salt be soluble in the siloxane although insoluble salts may be employed if they are properly dispersed in the system. The dispersion may be carried out by employing a solution of the catalyst in a mutual solvent with the siloxane, or the catalyst may be dispersed on a filler and thereafter milled into the siloxane.

The term "carboxylic acid salt as employed herein includesthose salts which contain hydrocarbon radicals attached to the metal, for'example', dibutyl tin diacetate. 7 Specific examples of salts which are operative in this "invention are the 'naphthenates of the above metals such as lead naphthenate, cobalt naphthenate and zinc naph- 3 thenate, salts of fatty acids such as iron Z-ethylhexoa'te, lead 2-ethylhexoate and chromium octoate, salts of aromatic carboxylic acids such as dibutyl tin dibe'nzoate, salts of polycarboxylic acids such as dibutyl tin adipate and lead sebacate and salts of hydroxy carboxylic acids such as dibutyl tin dilactate.

In general, the amount of catalyst employed can be varied from .01 to 10% based upon the weight of the siloxane. A mixture of two or more of the defined salts may be employed if desired. The amount of catalyst varies from compound to compound depending upon the activity of the specific. compound in question and also.

the amount of catalyst will be varied depending upon the particular use for the product. For example, when a fast cure is desired, more catalyst is required- If one wishes to delay the cure, for example, in applications where extensive fabrication time is required less catalyst is used.

a In general, catalyst concentrations of from .2 to 2% based on the Weight of the siloxane are suflicient.

If desired, fillers can be incorporated into the elaslatterfillers are preferred in those applications requiring elastomers of this invention can be cured in a press at temperatures of 150 C. to. 250 C. The products can be hot or cold molded and extruded, although in carrying out extrusion operations. care should be taken that the curing does not advance too far prior to extrusion.

The products of this invention are particularly adaptable for potting compounds. For example, a fluid polymer of say 10,000 cs. may be compounded with the silicate and, if desired, enough filler so that the material can still be poured. The catalyst may then be added and the material poured into the container whereupon it will set in a matter of a day or less to a rubbery material which will completely fill the voids in the apparatus.

The materials of this invention have heat stabilities comparable with that of previously known siloxane elastomers. This is exhibited by little reduction of physical properties after heating at 250 C. and also by low weight loss during heating. Furthermore, the stress-stfain'pfoperties of some of the elastomers of this invention-are far superior to those of any known siloxane elastomer.

The elastomers of this invention are useful for electrical insulation, for sealing of voids and for any other use Where elastomeric products are needed.

It should be understood that the claims include within their scope nonessential ingredients such as oxidation inhibitors, compression set additives, pigments, fillers and other specialized ingredients normally employed in siloxane elastorners.

The following examples are illustrative only and should not be construed as limiting the invention which is properly delineated in the appended claims. In all'of the examples the parts are parts by weight.

Example .1 p

In each of the runs of this example 100 parts by weight of a nonflowing benzene soluble dimethylpolysiloxane was milled with 50 parts by weight diatomaceous earth, 5 parts by weight of a devolatilized ethylpoly- .hightemperature stability. If employed, the amount of .filler may rangefrom 10 to 300 or more parts by weight based on the weight of the polysiloxane. a The. elastomers of this invention may be compounded in the usual manner for compounding siloxane elastomers.

,If'the materials are to be stored prior to, use, itis necesfiller, and carboxylic acid salt and then add the silicate just prior-to use.

. The latter method is particularly valuable in' coating applications where a mixture of polymer, salt, and if desired, a filler can be applied to the base member and thereafter a coating of the silicate can be applied in any convenient manner such as by brushing, spraying and the like. The silicate will diffuse into the polysiloxane coating and curing in situ will thereupon occur.

Curing of the elastomers of this invention takes place spontaneously. at roorn temperature upon mixing the "sil'o xana silicate. and carboxylic acid salt. T he curing in general will require from one to three days at room temperature. 'If desired, the ,curing'tim e can be increased by'maintaiuingthe mixturejat a temperature below room temperature, for example, at 0C. or the curing time can be decreased by employing elevated temperatures.

It is to be understood, of course, that "ifde'siredpthe silicate, and the various catalysts in the various amounts shown in the table below. After milling the product was cold'molded into a sheet and allowed to age at room temperature for thetime specified. The physical properties were then determined.

Physical Properties Time Catalyst Amount 1 in Day's; Tin Percent D p.s.i. Eat- Break Lead 2-ethylhex0ate 1 1 46 583 383 Dibutyl tin diacetate .;5 '1 @603 350 D .;2 I 40 146 340 1 1 683' 313 .5 1" .43 ,477 ,345 a .2 1 33 632 625 -1 l 46 578' 270 .5 1 9 543 330 1 D0 .2 V w l 41 533 120 Butyl tin tri-Z-ethylhexoate 5 1 477 r 345 Iron Z-ethylhexoate 1 a 1 35 321 39? Cobalt 2-ethylhexoate 1 1 35' 1 330 380 Manganese 2-ethylhexoate. 1 :2 22 '117 510 Zinc 2-ethylhexoate 5 2 Set'to an elastoi meric product.

Amount of catalyst is expressed in parts by weight based'on the weight of partspolysiloxane.

Example 2 100 parts of a benzene soluble dimethylpolysiloxane,

35 parts of a silica powder which had been prepared by determined" as shown.

Physical Properties Curing Time In Days '1 1n Percent D p.s.l. E

Break The above experiment was repeated except that .5 part lead Z-ethylhexoate was employed as a catalyst. The properties upon aging were as follows:

. Example 5 100 parts of a 2.000 cs. viscositypolysiloxane having the composition 7.5 mol percent phenylmethylsiloxane and 92.5 mol percent dimethylsiloxane, which polymer ,was' free of'triorganosilyl end groups, 80 parts by'weight of ground quartz having a particle size 'less than microns, 3 parts of ethylpolysilicate and .5 part of lead 2-ethylhexoate were milled and then poured into a container. After 24 hours at room temperaturethe material" had set to a rubbery elastomeric material. After the material had stood for 3 days at room-temperature it was then heated 1 hour at 150 C. and 1 ,hour at 250 C. whereupon the weight loss was only 1.6%.

This material is suitablefor use as an electrical potting properties upon agingwere as follows:

I Physical Properties Curing Time In Days T in Percent D p.s.i. E at I Break Example 4 100 parts 'of a 15,000 cs. dimethylpolysiloxane which was made by polymerizing dimethylsiloxane cyclics with KOH.HOCH(CH at 150 C., 80 parts ground quartz having a particle size less than 40 microns, 3 parts ethylpolysilicate and .5 part lead 2-ethylhexoate were milled until a uniform mix was obtained. The product was then molded into test bars at elevated temperature and in the table. 1

Orthosilicate: Durometer n-Amylorthosilicate 22 Allylorthosilicate 42 n-Butylorthosilicate 24 n-Propylorthosilicate 22 After 7 days the product was heated 24 hours'at 250 C. whereupon the properties were D 23, T 233 p.s.i. and percentE at break 313.

15 compound. Physical Properties Exam? 1 v curing Timemmys Elastomeric products are obtained when parts by D T1 1 Pg rce .weight of 100,000 cs. polysiloxanes having the composii 20 tions shown below are compounded with 3 parts by weight of thepolysilicates shown below and 2 parts by 31 850 1,255 weight dibutyl tin diacetate and thereafter allowed to 34 1,184 1 1,175 39 1 640 1, 150 stand at room temperature 41 1,720 1,170 44 Z070 L400 25 Slloxane Polyslllcate By way of comparison, the identical polymer and the t e iO Methylpolysilicate. identical filler in the same amounts shown above were Etsxo Iswmpylmlysm? milled with 15 parts of weight benzoyl peroxid and 90 mol percent MezSiO and 10 mol percent Ethylpolysilicate. cured by heating for 5 minutes at C. The proper- 30 Y ties of the vulcanized elastomer were D 42, T in p.s.i. O- 1320 and percent E at break 860. Thus it can be seen that the elastomers of this invention give substantially 90 1110! Percent M 2 and 10 11101 p e Dobetter properties than a comparable peroxide vulcanized Me f i l elastomer. E l 3 v 35 CHrCHsiO xamp 9 Fr- FGl 100 parts of a benzene soluble dimethylpolysiloxane, (clamvMesion; I 40 parts of a fume sheet, .5 part ferr1c oxide, 20 parts Q Q T g -h gy po y i icate. de'volatilized ethylpolysilicate and 1 part lead '2 ethyl- 40 fi P t yslcate hexoate were milled and cold pressed mto a sheet. The

Example 7 Each of the compositions employed in this example were as follows: 100 parts of a dimethylpolysiloxane fluid of 15,000 cs. viscosity which was essentially free'of trimethylsiloxy endblocks, 30 parts by weight.diatoma-' ceous earth, 0.5 part lead Z-ethylhexoate. and 1.5 parts of the orthosilicates shown below. In each case the ingradients weremixed and the mixture allowed to stand 24 hours at room temperature whereupon eachmixture set to a rubbery product having a durometer as indicated Each ,of the above compositions cured to a rubbery solid in one hour at C.

That which is claimed is: v

1. A cured polysiloxane elastomer obtained from a mixture of ingredients consisting essentially of (1) an organopolysiloxane of at'least 100 cs. viscosityat 25 C.,

said siloxane being composed of polymer units of the I formula R,,SiO

. T where R is selected from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and n has an average value from 1.99 to 2 inclusive, (2) from .1 to 5.0% by weight based on the weight of the siloxanev of a hydrocarbonoxy sili- "'7 cate in which the hydroc'a'rbc'ini-adicals are monovalent aliphatic hydrocarbon radicals of less than 8 carbon atoms, and (3) from .01 to byweight based on the weight of the polysiloxane of a carboxylic acid salt of metals ranging from lead to' manganese inclusive in the electromotive series 'offmetals, in which salt the acid radicals have less than 16 carbon atoms.

2. A 'ciired polysiloxane elastomer obtained from a mixture of ingredients consisting essentially of (1) an organopolysiloxane of at least 100 cs. viscosity'at "'C.. said siloxane being composed of polymer units of the formula R SiO where R is selected from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and n has anfaverage value from 1.99to'2 inclusive, (2) from .1 to 50% by weight based on the weigbtof the snexa e of a hydrocarbonoxy orthos'ilicate'in which the hydrocarbon radicals are monovalent aliphatic hydrocarbon radicals of less than 6 car-- bon atoms, and (3) from .01 to 10% by weight based on the weight of "the polys'iloirane of'i'a carboxylic acid salt of metals ranging from lead to manganese inclusive in the electromotive series of metals, in which 'salt the acid radicals have less than 16 carbon atoms. g g

3. A cured elastomeric composition obtained from a mixture of ingredients consisting essentially of (1) a methylpolysiloxane of at least 100 cs. viscosity, said siloxane having an average of from 1.99 to 2 inclusive methyl radicals per silicon atom, (2) from .1 to 50% by weight based on the weight of the siloxane of n-propyl- 'orthosilicate, and (3) from .01 to 10% by weight based on the weight of the siloXane of a carboxylic-acid salt of metals of the group consisting of lead, tin and iron, in which salt the acid radicals have less than 16 carbon atoms.

4. A method of preparing siloxane elastomers which comprises mixing (1) an organopolysiloxane of less than 100 cs. viscosity at 25 Ct, said siloxane having a unit formula of R SiO T where R is selected from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and n has an average value from l.99 to 2'inclusive with (2) frotn l to 50% by weight based on the weight of the siloiiane offa hydr'o- 5. The method of curing a polysiloxane which comprises applying to a base member a coating of a mixture of (1) an organopolysiloxane of at least 100 cs. viscosity sesame where R is selected from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and n has an average value from 1.99 to 2 inclusive, (2) from .1-% by weight based on the weight of the siloxane of a hydrocarbonoxy silicate in which the hydrocarbon radicals are monovalent aliphatic hydrocarbon radicals of less than 8 carbon atoms, (3) from .01 to 10% by weight based on the weight of the polysiloxane of a carboxylic acid saltof metals ranging from lead to manganese inclusive in the;

electromotive series of metals, in which salt the-acid radicals have less than 16 carbon atoms, and (4) a silica filler.

7, A cured polysiloxane elastomer obtained from a mixture of ingredients consisting essentiallyof (1) an organopolysiloxane of at least cs. viscosity'at 25 C., said siloxane being composed of polymer units of the formula R- SiO where R is selected fromthe group consisting of monovalent'hydroc'arbon radicals and halogenated monovalent hydrocarbon radicals and n has an average value from 1.99 to 2 inclusive, (2) from .1 to 50% byweight based on the weight of the siloxane of a hydrocarbonoxy orthosilicate in which the hydrocarbon radicals are mono valent aliphatic hydrocarbon radicals of less than 6 carbon atoms, (3) from .01 to 10% by weightbased onthe weight of the polysiloxane of a carboxylic acid salt of metals ranging from lead to manganese inclusive in from a mixture of ingredients consisting essentially of v (1) an organopolysiloxane of at least 100 cs. viscosity at 25 C., said siloxane having the unit formula R SiO T where R is selected from the group consisting of mono- I valent hydrocarbon radicals and halogenated rnonovalent hydrocarbon radicals and n has an average value from 1.99 to 2 inclusive, (2) a'silica filler, (3) from L1 to 50% by weight based on the weight of the siloxane of sub stantially nonvolatile alkyl polysilicate in which the alkyl groups have less than 6 carbon atoms, and (4) from .01 to 10% by weight based on the weight of the siloxane of a carboxylic acid salt of metals ranging from lead to manganese inclusiveiin the electromotive series of i metals, said carboxylic acid containing less than 16 car.-

carbon radicals and halogenated monovalent hydrocar bon radicals and n has an average value from 3.99 to inclusive, (2) from .01-to 10% by weight'based on the weight of the siloxane of a carboxylic acid salt of metals ranging fro'm -ladto ina'gsaese inclusive in the et'ectromotive'series of metals,' said carboxylicfacid containing less than '16- carbon "atoms and thereafter applying to s'aidco'ating (3) from'.1'to 50% by ,weightbased on the weight o'f -the "silonarie' of "a hydro'carbonoxy silicate in bon atoms.

9. A cured elastomeric composition of'matter obtained from a mixture of ingredients consisting essentially of (1) a methylpolysiloxane of at least 100 cs. viscosity at 25 C., said siloxane having an average of from 1.99 to 2 inclusive methyl groups per silicon atom, (2 a silica filler, (3) from .1 to 50% by weight based on the weight of the siioxane of substantially nonvolatile ethylpolysilicate, and (4) from .01. to 10% by weight based on the weight'of the s'iloxan'e'ofa carboxylic acid salt of metals of the group consisting of lead, ,tin and iron, said carboxylic acid containing less than "16 carbon atoms.

9 10. A cured elastomeric composition of matter obtained from a mixture of ingredients consisting essentially of (1) a polysiloxane of at least 100 cs.. viscosity at 25 C. having an average of from 1.99 to 2 inclusive methyl groups per silicon atom, (2) a silica tiller (3) 5 from .1 to 50% by weight based on the weight of the siloxane of n-propylorthosilicate and '(4) from .01 to 10% by weight based on the weight of the siloxane of a carboxylic acid salt of metals of the group consisting of lead,

tin and iron, said carboxylic acid containing less than 10 16 carbon atoms.

UNITED STA'EES PATENTS Hyde Oct. 9, 1951 Dexter Feb. 28, 1956 Smith-Johannsen May 8, 1956 Talcott Aug. 21, 1956 Currie et a1. Nov. 26, 1957 Berridge July 15, 1958 

1. A CURED POLYSILOXANE ELASTOMER OBTAINED FROM A MIXTURE OF INGREDIENTS CONSISTING ESSENTIALLY OF (1) AN ORGANOPOLYSILOXANE OF AT LEAST 100 CS. VISCOSITY AT 25*C., SAID SILOXANE BEING COMPOSED OF POLYMER UNITS OF THE FORMULA
 6. A CURED POLYSILOXANE ELASTOMER OBTAINED FROM A MIXTURE OF INGREDIENTS CONSISTING ESSENTIALLY OF (1) AN ORGANOPOLYSILOXANE OF AT LEAST 100 CS. VISCOSITY AT 25*C., SAID SILOXANE BEING COMPOSED OF POLYMER UNITS OF THE FORMULA 